After the Earth, Mercury is the second densest planet. Despite its small size, Mercury is very dense because it is composed mainly of heavy metals and rock.

Mercury is named after the messenger of the Roman gods, who is also known as Hermes in Greek mythology. This is because of the speed in which Mercury orbits the Sun and the speed with which Mercury the Roman deity was able to deliver messages.

It was once believed that a planet called Vulcan existed between the orbit of Mercury and the Sun – however the existence of such a planet was never found.

Mercury is the only planet which doesn’t rotate exactly once every year – instead rotating three times for every two orbits of the Sun. This is because it is nearly tidally locked to the Sun.

One day on Venus is longer than one year. Due to the slow rotation on its axis, it takes 243 Earth-days to complete one rotation. The orbit of the planet takes 225 Earth-days – making a year on Venus shorter on day on Venus.

The temperature on Venus doesn’t vary much between the night and day. This is due to the slow movement of the solar winds across the surface of the planet.

Venus has a very weak magnetic field. This surprised scientists, who expected Venus to have a magnetic field similar in strength to Earth’s. One possible reason for this is that Venus has no solid inner core, or that its core is not cooling.

Venus orbits the sun in an ellipse, but its orbit is the closest to being a circle out of all the planets in the Solar System.

The Earth was once believed to be the centre of the universe. For 2000 years ancient astronomers believed that the Earth was static and had other celestial bodies travelling in circular orbits around it.

Earth’s water was initially trapped within the planet. Over time the Earth’s water was brought to the surface by the planet’s volcanic activity.

The highest point found on Earth is Mount Everest which reaches a height of 8.8 km.

The lowest point on Earth is called Challenger Deep and at 10.9 km below sea level, it is further than the peak of Mount Everest.

Mars is the only other planet besides Earth that has polar ice caps. The northern cap is called the Planum Boreum, with Planum Australe in the south. Water ice has also been found under the Martian ice caps.

Mars has seasons like Earth, but they last twice as long. This is because Mars is tilted on its axis by about 25.19 degrees, which is similar to the axial tilt of the Earth (22.5 degrees).

Mars does not have a magnetic field – although there are some scientists that believe it did have a magnetic field somewhere around 4 billion years ago.

The orbit of Mars is the most eccentric of the eight planets. This means it is the least circular orbit path of the planets.

Jupiter has the shortest day of the eight planets. The planet rotates very Jupiter rotates very quickly, turning on its axis once every 9 hours and 55 minutes. This rapid rotation is also what causes the flattening effect of the planet, which is why it has an oblate shape.

Jupiter has a very unique cloud layer. The upper atmosphere of the planet is divided into zones and cloud belts which are made of ammonia crystals, sulfur and a mixture of these two compounds.

If Jupiter had become 80 times more massive, nuclear fusion would have occurred in its core. Had that happened, it would have become a star instead of a planet.

Jupiter does not experience seasons like other planets such as Earth and Mars. This is because the axis is only tilted by 3.13 degrees.

In Roman mythology Saturn was the father of Jupiter, king of the gods. This relationship makes sense given that the planets Saturn and Jupiter are similar in so many respects, including size and composition. The Greek counterpart is known as Cronus.

Saturn gives off more energy than it receives from the Sun. This unusual quality is believed to be generated from the gravitational compression of the planet combined with the friction from large amount of helium found within its atmosphere.

Saturn has the fastest winds of any other planet in our solar system. These winds have been measured at approximately 1,800 km per hour

Saturn is the flattest of the eight planets. With a polar diameter that is 90% of its equatorial diameter, Saturn is the flattest of all the planets.

Uranus rotates on its axis once every 17 hours and 14 minutes. Like Venus, it turns in a retrograde direction which is opposite to the direction Earth and the other six planets turn.

A collision may have caused the unusual tilt of Uranus. The theory is that an Earth-sized planet may have collided with Uranus which forced its axis to drastically shift.

The mass of Uranus is about 14.5 times the mass of Earth, making it the lightest of the four gas giants of the outer solar system.

The Voyager 2 is the only spacecraft to have flown by Uranus. This happened in 1986 and it flew past the planet at a distance of around 81,500 km. This mission returned the very first close-up images of the planet, its ring system and its orbiting moons.

Neptune also has a second storm called the Small Dark Spot. This storm is around the same size as Earth’s moon.

Neptune spins very quickly on its axis. The planets equatorial clouds take 18 hours to complete one rotation. The reason this happens is that Neptune does not have a solid body.

Like the other outer planets, Neptune possesses a ring system, though its rings are very faint. They are most likely made up of ice particles and grains of dust with a carbon-based substance coating them.

The climate on Neptune is extremely active. In its upper atmosphere, large storms sweep across it and high-speed solar winds track around the planet at up to 1,340 km per second. The largest storm was the Great Dark Spot in 1989 which lasted for around five years.